Thiols
Hops and Thiols
Citra and Hallertau Blanc have the highest odour unit of free 3SHA (Fermentis seminar)
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Thiols
Nerol
- A monoterpene alcohol with a rose and citrus aroma. An isomer of geraniol. Not usually detectable by YCH analysis.
β-citronellol
- A monoterpene alcohol with an aroma similar to citronella candles. Not thought to be found in hops, but has been detected in beer. It is believed that this compound is produced by metabolism of geraniol by yeast during fermentation.
SULFUR-CONTAINING COMPOUNDS
Sulfur compounds represent an increasingly important area of study in hop aroma science. They are difficult to detect using a traditional GC-MS and are usually found in extremely small concentrations in hops, potentially two orders of magnitude less than terpenes (ASBC). However, the human nose is excellent at detecting sulfur compounds. An example: the aroma threshold for myrcene is about 20ppb, while 4MMP (a common sulfur compound found in hops) is detectable at around 0.05ppb, or about 400 times less (ASBC)! Sulfur-containing compounds are now thought to be an integral part of the aroma profile of a beer, incentivizing brewers to harness their power in the brewing process. Common confusion surrounds the prefixes mercapto and sulfanyl, which are generally interchangeable. Using mercapto- is not now suggested by the IUPAC. However, much of previously completed research on sulfur-containing compounds use the mercapto- prefix, along with much of modern brewer parlance. In the following descriptions, the sulfanyl- prefix will be used in text, but the mercapto- abbreviation will also be listed. Polyfunctional Thiol or Thiol
Polyfunctional Thiol or Thiol
In chemistry, a blanket term for an organic compound containing a sulfhydryl functional group(-SH). In the brewing world, it is a broad term covering a group of compounds, often contributing positive beer flavor and aroma.
4-methyl-4-sulfanylpentan-2one (4MSP or 4MMP)
- A polyfunctional thiol, and one of the better-known sulfur compounds in the brewing world. Research suggests that 4MSP is not present in European varieties (Kishimoto, Morimoto, Kobayashi,Yako, & Wanikawa, 2008). 4MSP is usually described as having a blackcurrant aroma. At higher concentrations the aroma can become unpleasant, expressing as a “catty” or cat-urine-like.
- Interestingly, the threshold at which 4MSP becomes unpleasant varies substantially among individuals, similar to the flavor perception of cilantro. When dissolved in a beer matrix, it is thought to add tropical and wine grape-like flavors.
3-sulfanylhexan-1-ol (3SH or 3MH)
- A polyfunctional thiol commonly found in hops. It has a tropical and grapefruit aroma. 3SH can be converted by yeast into 3SHA (3MHA).
3-sulfanylhexyl acetate (3SHA or 3MHA)
- This compound is found readily in hoppy beers, but not usually found in hops (Kishimoto, Morimoto, Kobayashi, Yako, & Wanikawa, 2008) . Like its relative 3SH, it has a grapefruit and tropical aroma. When present in high concentrations it can provide a passionfruit flavor. Whirlpool and activefermentation dry hopping additions containing varieties high in 3SH are thought to maximize the potential for 3SHA by maximizing contact time between hop compounds and actively fermenting yeast.
3-sulfanyl-4-methylpentyl acetate (3S4MPA or 3M4MPA)
- A polyfunctional thiol with a rhubarb and grapefruit aroma. In a study by Takoi Et al. on Sauvignon Blanc wines, it was concluded that 3S4MP and 3S4MPA worked synergistically to enhance flavor (Takoi, et al., 2009).
3-sulfanyl-4-methylpentan-1-ol (3S4MP or 3M4MP)
- A polyfunctional thiol with an aroma of rhubarb and grapefruit. It has an extremely low odor threshold of 0.07ppb. Like 3SHA, its concentration increases during fermentation (ASBC).
ESTERS AND KETONES
2-methylbutyl isobutyrate
- An ester derived from hops which typically survives the brewing process. Like most esters, it lends a fruity aroma, specifically apricot.
2-nonanone
- A ketone with a variety of different aromas. It can range from sweet and fruity to cheesy, buttery, and waxy.
Methyl geranate
- A methyl ester derived from hops which typically survives the brewing process into finished beer. It lends a fruity and floral aroma and is usually the only hop-derived methyl ester that survives into beer.
Butanoic acid 3-methylbutyl ester
- An ester derived from hops which typically survives the brewing process. It lends a fruity, sweet, and tropical aroma.
Averado and Berkley yeast tests
Thiol Test Recipes
Cold Pressed Hazy IPA
- 2-Row Malt for Base, 25% malted wheat & oats make up the grist.
- Mash Hopping with High Precursor Motueka Lot from Freestyle Hops, just 0.25 lbs / bbl.
- Whirlpool at 175, 0.75 lbs / bbl same Motueka lot.
- Ferment with Tropics yeast at 68 deg.
- Dry Hop 2.75 lbs / bbl with 40% HBC 586, 40% El Dorado, 20% Sabro Cryo.
- Centrifuged to less than 200 EBC
Contains No Juice Hazy IIPA
- 2-Row Malt for Base, 25% all wheat, incl. high protein red wheat from Mecca Grade. Mash Hopping with US Cascade Hops
- Whirlpool at 175, 2 Kg of Idaho 7 Full Spectrum Plasma & 0.5 lbs. / bbl Simcoe
- Ferment with Tropics yeast at 68 deg.
- Dry Hop 5 lbs / bbl with blend of Mosaic, Citra Cryo, Waimea & Nelson hops.
Takeaways – Brewing Process
- High-Precursor hops in Mash & Whirlpool (cooled to 175)
- Thiol Yeast for Fermentation (Tropics used in these examples).
- Moderate Dry Hop seems to prevent decrease of 3MH, although difference between 2.75 and 5 lbs was 2,000 ng/L – moderately perceptible. More efficiency with raw materials
- Comparing with Berkeley’s lab trials (unhopped): these beers were tested after packaging (3-4 weeks old), vs. Fresh and in the lab. Likely higher at packaging.
- At what point is the thiol threshold so far beyond perception that there’s little difference between x and y? (i.e. the “100 IBU” fatigue example). Odor Activity Values!
- Vengeful Barbarian shows importance / reliance of monoterpene alcohols to generate hop flavor. Thiols just part of the story.
- We know we’re going to get a TON of 3MH concentration from using thiol releasing yeast, focus on good hops to do the rest of the work.
Incorporating Thiols & Monoterpenes in Recipes
- Results from VB show us that Thiols are only part of the story. Must take into account:
- Presence of Monoterpene Alcohols: Geraniol, Linalool, Citronellol
- Ester compounds found in hops like 2MIB
- Knowing Free Thiols & Monoterpene Alcohol Concentrations, a brewer can extrapolate when planning dry hops.
- 1 Kg T90 Nelson hops / bbl = 1300 ng/L of potential 3S4MP if 100% extraction occurs.
- 1 Kg T90 Sabro Cryo hops / bbl = 497.84 ppm of potential Geraniol if 100% extraction occurs.
- Thinking about how much ”special sauce” could be going into your DH, rather than a blind lbs / bbl benchmark.
- Establish Odor Activity Values for various compounds, then determine how to get there with hops.
Trials with Thiol Yeast
Brewed a series of 5 bbl pilot batches to understand implications of bound thiols. First renditions to determine on sensory level the contribution of precursors from grain and minimal hopping. Amazing aromatic properties but unbalanced, “hollow” profile and unstable haze.
Tried a regular Hazy IPA recipe, not what we expected. Thiols took a back seat in the aroma, dry hop dominated & had a scrubbing effect. Complex flavor profile, could pick up the thiols on the palate. How do we front load wort with Thiol Precursors from hop products?
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Lager Yeast and Thiols
Malt and Hop as Sources of Thiol S Conjugates: Thiol-Releasing Property of Lager Yeast during Fermentation
ABSTRACT: The contribution of polyfunctional thiols (PFTs) to the overall flavor of a lager beer has been well documented, but their origin remains unclear. In comparison with Saccharomyces cerevisiae strains previously investigated (same conditions: 7 days at 24 °C, 3 days at 4 °C), we examined how Saccharomyces pastorianus yeasts are able to produce these PFTs from cysteinylated (Cys-) and glutathionylated (G-) conjugates. Up to 0.35% release was observed from G-conjugates against less than 0.08% for all yeasts studied so far. Lowering the wort nitrogen level and the fermentation temperature (12 °C) strongly increased the release efficiency and the ester/alcohol ratio from Cys-conjugates. However, it did not improve the release from G-conjugates and even prevented the yeast from producing any acetate. Although poor in free PFTs and their Cys-precursors, both Saaz hop and pale malt (classical ingredients for premium lager beers) confirmed to be significant sources of G-conjugates (especially those of 3-sulfanylhexanol and 3-sulfanyl-4-methylpentanol). …….
Yeasts. Four lager yeast strains (BRAS37, BRAS25, BRAS51a, and BRAS45; propagation in YPS liquid media at 28 °C) from the INBR UCLouvain collection (Louvain-la-Neuve, Belgium) and three active dry yeasts (SafLager S-23, SafLager W34-70, and SafLager S-189; hereinafter referred to as S23, W3470, and S189) from Fermentis Lesaffre (Marcq-en-Barœul, France) were used for fermentation trials …
After 7 days at 24 °C and additional 3 days at 4 °C, SafAle K-97 yeast reached the highest release efficiencies (up to 0.45 and 0.08% release from Cys- and Gconjugates, respectively). Significant differences were observed between yeast strains, especially in terms of the acetate ratio [released acetate/released (alcohol + acetate), varying from 0 to 80%]. This ratio was also greatly affected by wort density (higher esterification at 17 °Plato than at 15 and 12 °Plato).23 As for the nitrogen level of wort, known to greatly affect the ability of yeasts to release thiols in the oenological process (nitrogen catabolite repression of the gene for β-lyase Irc7p), the influence of this parameter has not been assessed under brewing conditions ….
Ability of Lager Yeasts to Release Thiols from SGlutathionylated Conjugates. Depending on the thiol nature, up to five of the lager yeasts (S23, W3470, BRAS25, BRAS51a, and BRAS45) were found to release free thiols from glutathionylated conjugates even more efficiently than SafAle K-97 (up to 0.36%)23 (Figure 2d−f). Surprisingly, no correlation emerged between the release from Cys-conjugates and the release from G-conjugates (e.g., S23 acted the most efficiently on Cys-conjugates and BRAS45 on G-conjugates). Yeasts BRAS37 and BRAS45 even exhibited a higher release efficiency with G-conjugates than with Cys-conjugates (also the case of BRAS25 for 3SPol conjugates). Yeast BRAS45 definitely stood out from the others, with release efficiencies reaching 0.36% for 3SPol + 3SPA, 0.23% for 3S4MPol + 3S4MPA, and 0.20% for 3SHol + 3SHA.
BRAS37, BRAS25, and BRAS45 showed a preference for 3SPol release; S23, W3470, and S189 for 3S4MPol release; and BRAS51a for 3SHol release. While some yeasts released these three thiols with similar efficiency, others exhibited a strong preference for one structure (e.g., BRAS25 released 0.34% 3SPol but less than 0.05% 3S4MPol and 3SHol)
……
Because the fermentation temperature for lager beers is usually around 10−15 °C, trials at 24 °C (see above) were compared with the ones at 12 °C. As illustrated in Figure 3a−c, lowering the fermentation temperature significantly improved (up to sixfold) the release from Cys-conjugates. Although acetate ratios were lower for 3S4MPA and 3SHA at 12 °C (Table 1), absolute acetate levels were much higher. The results for G-conjugates were quite different (Figure 3d−f): lowering the fermentation temperature to 12 °C caused only a slight (1.5-fold) increase in 3SPol and 3SHol concentrations, and no trace of the corresponding sulfanylalkyl acetates was detected. At 24 °C, release from G-conjugates was up to eightfold higher than from Cys-conjugates, whereas at 12 °C, release efficiencies for Cys- and G-conjugates were similar
……
The Complex Case of Thiols
https://beerandbrewing.com/the-complex-case-of-thiols/
4-mercapto-4-methylpentant-2-one (4MMP), smells and tastes of box tree, black currant, and ribes. It is also known as 4-methyl-4-sulfanylpentan-2-one (4MSP). Another, 3-mercaptohexan-1-ol (3MH), is often described as exotic, smelling of rhubarb and citrus. And the third, 3-mercaptohexyl acetate (3MHA), is reminiscent of passion fruit and guava.
…..
As reported in “Hops Oils & Aroma: Uncharted Waters” (Craft Beer & Brewing Magazine®, March/April 2016), a team at Sapporo Breweries in Japan conducted a study in 2012 in which they compared the compositions of monoterpene alcohols in various hops, examining the behavior of geraniol and citronellol under various hopping and hops-blend conditions. Among other things, their experiments demonstrated that the co-existence of linalool, geraniol, and citronellol could increase the perception of “citrus” in a model solution. Anecdotally, using this information, adventurous brewers combined hops high in linalool (such as Bravo or Nugget) with others rich in geraniol (for instance, Chinook) to brew beers they described as fruity, sometimes tropical. But it turns out linalool, geraniol, and citronellol may not have been totally responsible for those flavors.
Following additional research, the team from Sapporo has a new hypothesis. In their experiments, sensory panelists rated various aroma attributes of a solution dosed with 4MMP, scoring it two (out of four) for “tropical.” Similarly, a solution dosed with a mixture of linalool, geraniol, and citronellol scored less than two for tropical. However, when all four were blended, the tropical score jumped to a full four. (That may be what happens when brewers use Chinook because not only is it geraniol-rich, it also contains 4MMP.)
Malts
Escarpment found that with their Thiol Libre yeast if you use pilsner malt, especially N.American pilsner, it can have an unpleasant ester. Also when ferm temps get above 22 it becomes Belgiany
Thiols and Oxidation
The team at Deschutes Brewery ran a shelf life study using dry-hopped Thiolized beer in an effort to discover whether the presence of thiols had any impact on the perception of oxidation, hop flavor, and fruit flavor. What they found was that when compared to a fresh sample, dry-hopped Thiolized beer maintained its stability after two months. It decreased in sulfur character after 0 – 1 month (from BBT to 1month-old cans). It increased in fruit scoring from 0 – 2 months (from BBT to 2month-old cans).
